This invention relates to the preparation of espresso coffee, or Italian coffee, by percolating boiling water through a certain lightly pressed quantity of ground roasted coffee in powder form.
It is equally suitable for preparing espresso coffee starting from a single-measure or multi-measure coffee sachet formed of heat-resistant material able to act as a filter.
The invention is also suitable for preparing drinks from coffee substitutes, such as barley or the like.
Hereinafter, reference will be made exclusively to coffee, this term also embracing its substitutes.
Espresso coffee preparation machines for domestic or bar use comprise a hot water generator feeding a percolation chamber containing the coffee powder.
Said chamber commonly comprises the lower filtering wall, for example of perforated stainless steel, and is connected below a top piece through which the boiling water is fed.
Below the filtering wall there is defined a collection chamber for the percolated product which flows to the outside through a spout below which the cup is placed.
The quality of the product obtained depends both on the quality of the powder and on the ability of the operator, who has to press the powder to the correct extent to achieve uniform distribution of the percolating water through the entire coffee mass.
A commonly observed indicator in the user""s judgement of the quality of the espresso coffee is the presence of froth, ie a creamy phase above the surface of the liquid phase.
The need to optimize the percolation stage, on which for equal powder quality the quality of the finished product depends, is obvious.
In the known art, in spite of full operator attention, there is a limit to the degree of utilization of the powder, as almost inevitably passages of lesser density form in the powder mass, creating preferential passageways for the hot water, which hence does not sufficiently traverse certain parts of the powder.
Said drawback is also present in automatic machines, in which the manner in which the powder is fed to the percolation chamber often does not ensure uniform water passage through the whole of the coffee powder.
The object of this invention is to propose and provide an espresso coffee preparation method and device which ensures maximum powder utilization and can be easily adapted for the use of any starting substance.
The invention is aimed at both manual machines and automatic machines.
The invention is primarily based on the fact of creating a back pressure of desired value which slows down the flow of the hot water, giving it time to expand throughout the entire mass of powder.
According to the invention, said back pressure is preferably associated with an emulsifying chamber positioned between the liquid exit nozzle and the coffee delivery spout, the liquid entering this chamber with certain speed to mix with the air and produce a creamy emulsion giving an enhanced appearance to the drink.
The method of the invention is implemented by devices easily associated with manual or automatic machines.
Said devices enable the object of the invention to be attained by virtue of the characteristics stated in the claims.